SGPWhat it is: The student growth percentile (SGP) is one of several measures that have caught on with the rise of data-driven school reforms, providing not just a snapshot of student achievement but also a gauge of its progress. Widely used in nearly two dozen states, SGPs are not without their critics, who contend test scores do an injustice in judging school and teacher performance.

What it is — exactly: The SGP is a measure for each student in a school in how he or she performs on state tests from one year to the next as compared to other students across the state with similar achievement levels.

Albert, an example: The state in its presentations uses the example of a hypothetical student named Albert, who scored as a fourth-grader a 160 on the state’s NJASK test (out of a maximum of 300 points). In fifth grade, he then scored a 165. That still left him in the “partially proficient” range, but among all fifth graders who had scored 160 the year before, the five-point gain was better than 70 percent of his peers. His SGP then was 70.

How its used to grade schools: In its new School Performance Reports, the state is now using the SGP as a measure for student achievement in a school as a whole, in addition to the standard proficiency rates that have been publicized for more a decade. The state’s methodology takes the median SGP of all students in a school who took the tests, and comes up with a single score.

Now for teachers: For the first time, the state will assign every applicable teacher a median SGP for the year. The state is providing a test run of those scores for 2012-2013, with plans to have actual scores applying to teacher evaluations for 2013-2014. The scores will apply to about 20 percent of all teachers in the state, given the limited number of teachers who have students taking the state tests in their subject areas. The first year is also only a practice, officials said, but ultimately it will count for 30 percent of a teacher’s overall evaluation.

Not public: The state’s new tenure law, which has created the new evaluation system, requires that individual teacher’s scores are kept confidential and are not to be released to the public.

What else counts: Under the new tenure law, student performance measures cannot count for more than 50 percent of a teacher’s overall evaluation. Beyond the SGPs, the balance of the evaluation is through individual, untested student performance measures called student growth objectives (SGOs) that are set individually by teachers and their supervisors.

A few caveats: There are limits to the SGP, some obvious, some more technical. Given that not all students take the state tests, the SGP currently only applies to students who take the tests for two consecutive years, meaning only Grades 4 through 8. The state’s high school test is now only given in 11th grade, meaning SGPs don’t yet apply to high schools. In addition, the state excludes students who were not in school for at least 70 percent of the year.

Extra caveats for teachers: As the median SGP begins to be applied to teacher evaluations, there are a few other controls. If there are fewer than 20 students with SGPs in a given teacher’s classroom, the SGP is not applied at all. And if a teacher was in the classroom for less than 60 percent of the year, the SGP also doesn’t apply.

The debate: The SGP is one of a number of student growth measures that have been criticized by those who contend that it does not accurately measure a student, school, or teacher performance. The critics are many, including the state’s dominant teachers union, the New Jersey Education Association, which has lobbied hard against an over-reliance on the SGP or any other measure.

The academic debate: Much of the debate has been among researchers on both sides. The model’s main architect is Damian Betebenner of the National Center for the Improvement of Educational Assessment in Dover, NH. Among the chief critics is Bruce Baker, a professor of education at Rutgers University. Baker contends in his research that the SGP is deeply flawed as a measure, biased against schools and teachers of low-income and other disadvantaged children.